Another nice application of USB memory devices comes from "Any User Global," who slapped IP phone software in one, added a earphone-mic jack, and called it a day (and the "World's Smallest IP Phone"). Called the "ImPhone," this USB key contains IP phone software (which appears to be pretty standard) that will automatically be installed and launched when the key is inserted into any Windows XP or 2000 machine. If the machine doesn't have a microphone and speakers already, you're still good; the ImPhone features a minijack for connecting the included earphone/microphone device. I'd go bananas for a Skype version of this.
Product Information [Any User Global]